Water Reduction credit points for for ID +C seem unusually high

We are working on a project where the building exists and are finishing out the interior, thus ID +C. It seems to get any credit points for this category, a grey water collection system has to be introduced. I assume that many ID + C projects are in the same situation - an existing building in place. My MEP says that placing a grey water tank on site would cost tens of thousands of dollars. Collecting rooftop rainwater for commercial projects in the state of Colorado is illegal, so not an option. I could see that if this were a NC project where there is overall site construction that incorporating a grey water tank would be viable, but for buildings that already exist in place it seems extremely costly for any credits. Why is Water Reduction weighted so heavily for ID +C? We will have to write off 12 credit points because of this. Thank you.